N-Carboxymethyl chitosan

Co-administration of ofloxacin and chitosan in eyedrops increased the bioavailabUity of the antibiotic [290]. Trimethyl chitosan was more effective because of its solubility (plain chitosan precipitates at the pH of the tear fluid). On the other hand, N-carboxymethyl chitosan did not enhance the corneal permeability nevertheless it mediated zero-order ofloxacin absorption, leading to a time-constant effective antibiotic concentration [291]. Also W,0-carboxymethyl chitosan is suitable as an excipient in ophthalmic formulations to improve the retention and the bioavailability of drugs such as pilocarpine, timolol maleate, neomycin sulfate, and ephedrine. Most of the drugs are sensitive to pH, and the composition should have an acidic pH, to enhance stability of the drug. The delivery should be made through an anion exchange resin that adjusts the pH at around 7 [292]. Chitosan solutions do not lend themselves to thermal sterilization. A chitosan suspension, however. 

Cancer-risk-diet relationship, 262 Canonical correlation analysis, 104 Capsaicin, 15-16 N-(Carboxymethyl)chitosan, preservation of meat flavor, 73 Carrageenan, fat replacement in ground beef, 73-75 Carry-over, description, 57 Carry-through, description, 57 Carvone, headspace analysis, 24,25/ L-Carvone, chemicals resulting in anosmias, 211... 

Another approach to improve the properties of chitosan hydrogels is via the preparation of polymer composites. Porous hydrogels of N-carboxymethyl chitosan/polyvinyl alcohol were prepared by Lee et al. [99]. Hydroxypropyl chitosan was combined with sodium alginate for the formation of biodegradable hydrogels [100]. Chitosan-hyaluronic acid composite was prepared by Tan et al. [101]. 

Muzzarelli, R.A.A., Tanfani, F., Emmanueli, M., and Mariotti, S. 1982. N-(carboxymethylidene)chitosans and N-(carboxymethyl)chitosans Novel chelating polyampholytes obtained from chitosan glyoxylate. Carbohydr. Res. 107 199-214. 

Muzzarelli R.A.A., Weckx M., Filippini O., 1989. Removal of trace metal ions from industrial waters unclear effluents and drinking water with the aid of cross-linked N-Carboxymethyl chitosan. Carbohydr. Polym. 11 293-296. 

A NEW HEPARIN-LIKE SUBSTANCE SULFATED N-CARBOXYMETHYL CHITOSAN... 

For this purpose, we have used Euphausia superba chitosan to prepare N-carboxymethyl chitosan, and then we have submitted it to sulfation. Glyoxylic acid crystals were added to an aqueous suspension of chitosan powder, to obtain a chitosan glyoxylate solution (pH 3.2). Upon pH adjustement to 4.5 - 5.0, Schiff reaction took place with formation of N-carboxymethylidene chitosan. The latter was then reduced with sodium cyanoborohydride and isolated by addition of acetone. The thus obtained N-carboxymethyl chitosan was subsequently submitted to sulfation in N,N-dimethylformamide. 

The infrared spectrum of a sample of sulfated N-carboxymethyl chitosan insolubilized with acetone at pH 1.0 (hydrochloric acid) as well as a spectrum of sulfated N-carboxymethyl chitosan obtained by lyophilizing a solution of pH 8.3 show strong absorption bands at 1230 and 800 cm , assigned to the sulfate group they do not occur in the N-carboxymethyl chitosan spectrum (Fig. 2 of Ref,42). 

Sulfated N-carboxymethyl chitosan was dissolved in acetate buffer (50 mg/ml), submitted to sonication, filtered on 0.45 ym Millipore membranes and submitted to chromatography on Bio-Gel P-100. Since it is known that the average molecular weight and poly-dispersity are important parameters to be taken into account when testing a blood anticoagulant, we have developed this approach in order to reduce the molecular weight of the sulfated N-carboxymethyl chitosan, which originally was over 1,000,000 dalton. 

The elution peaks were centered at 39,000 and 80,000 dalton, and corresponded to about 25 % and 75 % of the sulfated N-carboxymethyl chitosan submitted to chromatography, respectively. Samples of sulfated N-carboxymethyl chitosan as prepared (without sonication, filtration and chromatography) and samples submitted to sonication and filtration were then tested for their blood anticoagulant activity. 

The tests carried out for the evaluation of the blood anticoagulant activity of sulfated N-carboxymethyl chitosan are the same as those for the determination of heparin, i.e. the antithrombin test for the thrombin inhibition and the heparin test for the factor Xa inhibition. Both of these tests were done by spectrophotometry at 405 nm on the p-nitroaniline liberated from a chromo-genic substrate. 

The results confirmed that sulfated N-carboxymethyl chitosan bound to antithrombin inhibits the thrombin present according to the following reactions ... 

Similarly, sulfated N-carboxymethyl chitosan forms a conqplex with AT, and inhibits factor Xa, thus proportionally decreasing the splitting of p-nitroaniline from substrate ... 

While sulfated N-carboxymethyl chitosans differing in terms of degree of acetylation, N-carboxymethylation and sulfation can be indicated as a class of heparin-like substances of interest for applications in vitro, it is anticipated that further refinements could lead to the preparation of sulfated N-carboxymethyl chitosans suitable for use in vivo. The main advantage obtained in using sulfated N-carboxymethyl chitosan instead of sulfated chitosan is in fact the demonstrated lack of adverse phenomena on cellular structures. 

Figure 1. A) Fragment of heparin, illustrating some characteristic structural features. B) Repeating units of sulfated N-carboxymethyl chitosan (I) present in minor amounts, (II) present at 42+ 4 %, (III) present at 58+4 %. Sulfur content, 11.0 %.

N-Carboxymethylidene chitosans and N-carboxymethyl chitosans novel chelating polyampholytes obtained from chitosan. Carbohydr. Res. 107 199 (1982). 

Sulfated N-carboxymethyl chitosans novel blood anticoagulants, to be published. 

Saym B, Somavarapu S, Li XW, Sesardic D, enel S, Alpar OH. TMC-MCC (N-trimethyl chitosan-mono-N-carboxymethyl chitosan) nanocomplexes for mucosal delivery of vaccine. Eur J Pharm Sci. 2009 38(4) 362-9. 

Saym B, Somavarapu S, Li XW, Thanou M, Sesardic D, Alpar HO, enel S. Mono-N-carboxymethyl chitosan (MCC) and N-trimethyl chitosan (TMC) nanoparticles for non-invasive vaccine delivery. Int J Pharm. 2008 363(l-2) 139-48. 

To overcome these limitations, chitosan has turned out to be a promising candidate as it sufficiently encapsulates the biomacromolecules and helps in their paracel-lular transport across the biological surface. Chitosan and some of its water-soluble derivatives such as N-trimethyl chitosan and mono-N-carboxymethyl chitosan have been used for improving the nasal and peroral absorption of various proteins, peptides and heparins via paracellular transport across the mucosa by opening the intercellular junctions [144-146]. 

Thanou, M., Nihot, M.T., Jansen, M., Verhoef, J.C., Junginger, H.E. Mono-N-carboxymethyl chitosan (MCC), a polyampholytic chitosan derivative, enhances the intestinal absorption of low molecular weight heparin across intestinal epithelia in vitro and in vivo. J. Pharm. Sci. 

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